High-fidelity column-type stereomonophonic diffuser with regulated sound deflection



United States Patent 3,241,631 HIGH-FIDELITY COLUMN-TYPE STEREOMONO-PHONIC DIFFUSER WITH REGULATED SOUND DEFLECTION The normal arrangementused to achieve stereophonic listening consists of two sound sources,either placed respectively at a certain distance to the left and to theright of the listener, or else assembled in a single unit, being fittedinto the sides of such a unit and directed towards the side walls of theroom so as to take advantage of sound reflections. However, as is wellknown, methods such as these do not give good results in rooms which areof modest size (such as ordinary living-rooms in modern houses) becauseof the multiplication of cross-reflections from the walls, which createan acoustic chaos and limit true stereophonic listening to a small areaof the room. Furthermore such methods lead to the creation of a socalledacoustic vacuum, that is to say the sounds seem to come only from theside and never from the centre; this in turn requires the setting-up ofa third sound channel.

With the diffuser which is the subject of the present discovery, theseinconvenience are avoided; it is suitable for stereo listening in smallrooms because it does not make use of reflection from the side walls (infact such reflections are a disturbance and are avoided), but usesreflection from the wall in front of the listener, he having thediffuser at his back, and thus brings about a displacement of thefrontal sound axis which is diverted sideways by the very high lateralbuildup of sound pressure.

Even though the invention is linked to a normal (left and right channel)amplifier, the acoustic vacuum is avoided by means of the front-facingloudspeakers. Furthermore, having a double vertical alignment ofloudspeakers one obtains the benefits of a column of sound" which hasmore or less cylindrical radiations and is therefore free from thepronounced initial drop in sound intensity found in the passage from thesound-source to the ear and, in addition, allows-for there is analignment of loudspeakers in continuous operation-the employment ofcommon, low-cost loudspeakers giving nevertheless extremely goodreproduction of low notes; with dual cone loudspeakers of 16 cm.diameter a range of 20 to 18,000 cycles/sec. was obtained.

Sound deflection, that is to say the displacement, towards the left andright sides, of the sound axis from the front loudspeakers, is obtainedby a mixture of the acoustic pressures set up by the lateralloudspeakers with that set up by the front loudspeakers. The resultanteffect of such acoustic pressures varies in direction according to thevariations in sound pressure ratios. With the present system it ispossible to regulate this sound deflection so as to obtain astereophonic listening-area of any predetermined amplitude and thereforethe diffuser is suitable for use even in rooms of small dimensions.Thus, for example, with a sound pressure ratio of 4 to l (i.e. lateralsound pressure 4, front sound pressure-1), the resultant sound beam isfound to be at about 37.5 degrees from the mean frontal axis, giving astereophonic listening area of 75% which, in practical terms, for a roomof 4 x 4 yards, means a stereo listening-area of 11 sq. yards if thediffuser is placed in the centre of the wall.

Since, furthermore, it is possible to make use of loudspeakers of smalldiameter, the unit can be of modest dimensions (the prototype, shown inthe attached drawing, measures 11.8 x 11.8 x 27.559 inches, employingloudspeakers of 6.299 inches diameter).

The results, therefore, are a unit of modest size, excellent low-rangefrequency response even when cheap loudspeakers are used, andstereophonic listening even in small rooms.

The attached drawing shows, by way of example, one practical form of thediffuser according to the present invention, in which:

FIG. 1 shows the invention in tranverse section.

FIG. 2 shows the front view.

FIG. 3 shows a right side view, the left side view being a mirror imageof this figure.

FIGS. 4 and 5 are two longitudinal section, frontal and lateralrespectively.

FIG. 6 is a view in perspective, reduced.

In normal use the holes in which the loudspeakers are mounted are invertical extending position.

The diffuser according to the present invention is mounted in a cabinet10 of wood or other material (plywood being recommended) with wallsthick enough to avoid vibrations, and is paralleloid in form (inpractice, a cylindrical form would also be satisfactory) having threevertical volumns of holes, one column in the front designated F in thefigures and a column on each of the two sides designated L and R forleft and right sides respectively. This cabinet is hermetically sealedon three sides. Internally it may be packed to a thickness of 1 or 2 cm.with a sound-absorbing material such as glass Wool, or the equivalent,especially at the rear and at the angles, to avoid echoes.

For aesthetic reason the cabinet may be covered externally with normalloudspeaker cloth and, for functional reasons, it may be provided withfeet so that it may stand, or with hooks for attaching it to the wall.

The number of holes, which must always be even, can vary, as can theirsurface area, according to the number and the size of the loudspeakerswhich are to be used. The centre of the front and of the side holes mustalways be on the same horizontal line (FIGS. 4 and 5) and, respectively,on the same vertical line. In practice, on the front section, instead ofa column of loudspeakers (FIG. 2) a double column of paired holes couldbe used.

The loudspeakers 25-28 of the left-hand sound channel are placed in theholes 21-24 of the left-hand lateral column and similarly loudspeakers35-38 of the righthand channel are placed in the holes 31-34 of therighthand .lateral column; in the front column are inserted loudspeakers15-18, alternatively for each channel, (e.g. loudspeakers 15 in hole 11of FIG. 2 for the right-hand channel, loudspeaker 16 in hole 12 for theleft-hand channel, loudspeaker 17 in hole 13 for the right-hand channeland so on); when a double frontal column is used, in the left-handcolumn the loudspeakers for the left-hand channel are placed, linked tothose of the left-hand lateral column; and similarly on the other side.

The loudspeakers can be of any type (normal or high-fidelity) of anydiameter, impedance, etc. However they must be linked so as to operatein phase and remain so through the whole frequency range; also,

besides the necessity of maintaining their polarity, it is essentialthat the distance between each of them is never greater than thediameter of the smallest of them; that is to say, less than D (FIG. 2).For example, if there are two loudspeakers with a diameter of 3 .9 and6.3 inches respectively, they must be set up so that the distancebetween them is not greater than 3.9 inches.

To prevent the frames of the frontal loudspeakers from interfering withthe sound-wave exchanges which occur inside the cabinet between thelateral loudspeakers (increasing or decreasing the intensity of thesound waves produced), the holes for the lateral loudspeakers must beoff-centred towards the back of the cabinet (FIGS. 3 and 5 Variations inthe number of the cones of the loudspeakers and in their diameter willdepend upon the low-frequency response required. For example, where dualcone loudspeakers are used with a single range from 80 to 18,000cycles/see, it will be sufficient to use four loudspeakers for eachlateral assembly. This will give a double range alignment (80:4:20) fromto 18,000 cycles/sec. It is advisable to use loudspeakers of differentdiameters so as to realise a more linear response to the frequenciesreproduced; provided they are in corresponding pairs, one for theleft-hand channel and one for the right. For example; if in theright-hand lateral assembly there is a loudspeaker of a given type,there must be a loudspeaker of identical type both in the other lateraland in the frontal assembly; again, to a certain type of loudspeaker inthe right-hand channel there must be linked one of identical type in thelefthand channel; thus, if at 11 in FIG. 2 there is placed a loudspeaker7.874 inches in diameter linked to the righthand channel, one of similardiameters linked to the lefthand channel must be placed at 12. It isobvious that the loudspeakers are set up in two groups, one for thelefthand channel and the other for the right. Such groupings may be madein series, in parallel, or mixed, this depending on the overallimpedance which may be required for each channel.

To achieve stereophonic effects in small rooms it is essential to bringabout a correct deflection of sound, that is to say an accuratedisplacement of the sound axis which results from the combination ofboth frontal and lateral sound pressures. The frontal loudspeakerscontribute the monophonic elements of the stereo programme and these godirectly to the listener, while the lateral loudspeakers displace to theright side and to the left the stereo elementsi.e. those contributed onthe right and left side respectively by the frontalloudspeakers-according to the rules governing the action of componentforces.

To achieve such displacement, the acoustic pressure exercised by thelateral loudspeakers must be greater than those exercised by the frontalloudspeakers. In practical tests a sufliciently large area ofstereophonic listing was obtained by Working with a lateral acousticpressure four times greater than the frontal (with such a 4:1 ratio theactual area of stereophonic listing can be calculated from the angle 75degrees approximately, which has as its point of origin the centre ofthe diffuser). This difference of acoustic pressure can be obtained invarious ways: thus one may vary the ratio between the surface area ofthe frontal and that of the lateral cones, or the ratio between theintensity of the magnetic fields (Gauss), or the ratio between the inputpotential of the frontal loudspeakers and that of the lateral ones. Ofthese ways, the last two are to be preferred to the first one. Inpractice, using loudspeakers which are all of the same type, the lastway is preferable, having, for example, the lateral loudspeakers fed inseries and connecting, in series with them, the frontal loudspeakersarranged in parallel. In such a sace the input current will pass rightthrough the mixing coils of the lateral loudspeakers and will thendivide so as to pass through the moving coils of the frontalloudspeakers.

In monophonic listing, all the loudspeakers work in base.

p To achieve efiicient results from the diffuser, that is to say toobtain a good stereophonic effect, it must be mounted so as to havebehind it a reflecting surface (i.e. a normal wall); it is not necessaryto place it in the centre of the surface, though it must never be placedin a corner. With a unit 27.5-31.4 inches high having feet 2.773.9inches long, one can obtain a good compromise between the spreading ofthe low notes, by means of the floor, and of the high notes which followset directions. As has been said, reverberations from the side walls ofthe room cause interference and acoustic chaos; they are, therefore, tobe avoided, whenever possible, by the hanging of curtains or similarmaterial, even if this is only done on a level with the diffuser.

What I claim is:

1. A high-fidelity stereo-monophonic sound diffuser comprising a cabinethaving openings in its front and on each side,

a loudspeaker attached at each opening,

said loudspeakers positioned in columnar alignment in the front and ateach side,

a right-hand channel electrically connected to said loudspeakerspositioned at openings on one side of said cabinet and at alternateopenings in the front of said cabinet,

at left-hand channel electrically connected to said loudspeakerspositioned at openings on the opposite side of said cabinet and atremaining alternate openings in the front of said cabinet,

and acoustic pressure between loudspeakers at openings on the sides ofsaid cabinet in comparison to loudspeakers at openings at the front ofsaid cabinet regulated so as to maintain a greater acoustic pressurefrom said loudspeakers at the openings in the sides of said cabinetwhereby said loudspeakers at the front openings are monophonic elementsand the stereophonic effects are the resultant of the acoustic pressuresfrom said loudspeakers at the side openings relative to the acousticpressures of said loudspeakers at the front openings.

2. The high-fidelity stereo-monophonic sound diffuser of claim 1,further characterized by a difference in the intensity of the magneticfields of said loudspeakers to regulate the acoustic pressure.

3. The high-fidelity stereo-monophonic sound diffuser of claim 1,further characterized by a difference in the input potential of saidloudspeakers to regulate the acoustic pressure.

4. A high-fidelity stereo-monophonic sound diffuser comprising a cabinethaving openings in its front and on each side,

a loudspeaker attached at each opening,

said loudspeakers positioned in columnar alignment in the front and ateach side,

a right-hand channel electrically connected to said loudspeakerspositioned at openings on one side of said cabinet and at alternateopenings in the front of said cabinet,

and a left-hand channel electrically connected to said loudspeakerspositioned at openings on the opposite side of said cabinet and atremaining alternate openings in the front of said cabinet,

said loudspeakers at openings at said one side connected in series andsaid loudspeakers at alternate front openings connected in parallel witheach other in a series connected with said loudspeakers at said oneside,

said loudspeakers at openings at said opposite side connected in seriesand said loudspeakers at remaining alternate front openings connected inparallel with each other in a series connection with said loudspeakersat said opposite side,

and acoustic pressure between loudspeakers at openings on the sides ofsaid cabinet in comparison to loudspeakers at openings at the front ofsaid cabi net regulated so as to maintain a greater acoustic pressurefrom said loudspeakers at the opening in the sides of said cabinet,

whereby said loudspeakers at the front openings are monophonic elementsand the stereophonic effects are the resultant of the acoustic pressuresfrom said loudspeakers at the side openings relative to the acousticpressures of said loudspeakers at the front openings.

References Cited by the Examiner UNITED STATES PATENTS 2,710,662 6/1955Camras 181-31 5 3,104,729 9/1963 Olson 181-31 FOREIGN PATENTS 1,130,8566/196-2 Germany.

272,869 1/ 1951 Switzerland.

LOUIS J. CAPOZI, Primary Examiner.

LEO SMILOW, Examiner.

S. J. TOMSKY, Assistant Examiner.

1. A HIGH-FIDELITY STEREO-MONOPHONIC SOUND DIFFUSER COMPRISING A CABINETHAVING OPENINGS IN ITS FRONT AND ON EACH SIDE, A LOUDSPEAKER ATTACHED ATEACH OPENING, SAID LOUDSPEAKERS POSITIONED IN COLUMNAR ALIGNMENT IN THEFRONT AND AT EACH SIDE, A RIGHT-HAND CHANNEL ELECTRICALLY CONNECTED TOSAID SAID CABINET AND AT ALTERNATE OPENINGS IN THE FRONT OF SAIDCABINET, A LEFT-HAND CHANNEL ELECTRICALLY CONNECTED TO SAID LOUDSPEAKERSPOSITIONED AT OPENINGS ON THE OPPOSITE SIDE OF SAID CABINET AND ATREMAINING ALTERNATE OPENINGS IN THE FRONT OF SAID CABINET, AND ACOUSTICPRESSURE BETWEEN LOUDSPEAKERS AT OPENINGS ON THE SIDES OF SAID CABINETIN COMPARISON TO LOUDSPEAKERS AT OPENINGS AT THE FRONT OF SAID CABINETREGULATED SO AS TO MAINTAIN A GREATER ACOUSTIC PRESSURE FROM SAIDLOUDSPEAKERS AT THE OPENINGS IN THE SIDES OF SAID CABINET WHEREBY SAIDLOUDSPEAKERS AT THE FRONT OPENINGS ARE MONOPHONIC ELEMENTS AND THESTEREOPHONIC EFFECTS ARE THE RESULTANT OF THE ACOUSTIC PRESSURES FROMSAID LOUDSPEAKERS AT THE SIDE OPENINGS RELATIVE TO THE ACOUSTICPRESSURES OF SAID LOUDSPEAKERS AT THE FRONT OPENINGS.